The U.S. Army ordered seven improved XB-7s as Y1B-7 for service testing. The new aircraft were fitted with improved Curtiss Conqueror engines with 75 more hp each. These engines were fitted with three-blade propellers also. Additionally, the corrugated fuselage skin of the XB-7 was replaced with smooth skin for the service test aircraft. These features combined to give the Y1B-7 a top speed of 182 mph, 13 mph faster than the XB-7.

The Y1B-7 was evaluated, but never entered quantity production. This was mainly due to the small bomb load and the better aircraft already being designed (i.e. Martin B-10).